1. Field of the Invention
The invention relates to a spindle in a machine tool, with an axis, a receptacle arranged in the axis and provided for a shaft of a tool holder, and a clamping mechanism for axial fixation of the shaft in the receptacle, whereby the clamping mechanism contains an axially movable clamping arbor and at least one segment arranged on a circumference of the clamping arbor, wherein by means of a first guiding acting between the clamping arbor and the segment the at least one segment upon axially shifting of the clamping arbor is radially movable between a first and a second operation position and fixes the shaft, in the first operation position, positively in the receptacle.
2. Related Prior Art
Such a spindle with such a clamping mechanism is known, for example from xe2x80x9cFZxe2x80x9d type machining centers of the applicant.
In known clamping mechanisms, the tool holder is inserted, with its outer taper, in a complementary taperbored receptacle of the spindle head. A clamping arbor of the clamping mechanism then enters into a corresponding receptacle in the shaft of the tool holder. The clamping arbor is axially movable via an axially arranged draw-in rod. For clamping of the tool holder, the clamping arbor is in an advanced operation position. On the outer circumference of the clamping arbor, several segments are arranged and distributed over the outer circumference. On the front end, the segments end up in a thickened head, which is, in this operation position, radially on the inner side. If, now, after insertion of the shaft into the receptacle of the spindle head, the draw-in rod is pulled back, the clamping arbor follows. Over a system of slide bevels, the segments then move radially outwards. The thickened heads then grip behind corresponding projecting parts in the receptacle in the shaft of the tool holder, so that the latter is axially positively fixed.
In axial direction behind the clamping arbor there is a crown with several recesses arranged and distributed over the circumference, in which recesses the rear ends of the segments are being held. The crown is in contact with the segments over further guide bevels. If the clamping mechanism is being clamped, the crown is pushed to the back against the force of a spring. If the clamping mechanism is released, the spring presses the crown to the front again, whereby the oblique guiding between crown and segments has the effect that these go back into their radially inner operation position.
In these usual clamping mechanisms, a malfunction can arise due to the fact that the segments, in their radially inner operation position (if the clamping mechanism is released) and in the interpositions between the two operation positions, too, take up undefined positions. This concerns particularly the axially front end of the segments. These can, for example, not return to their radially inner operation position, although the segments are correspondingly moved from the rear end by the crown moving forward under spring force. If, then, the segments are with their front end in an undefined position, there may be malfunctions when the next tool holder is inserted. In particular, an interlocking connection between tool holder and spindle receptacle can be reached, which has the effect that the tool holder already at this moment is entrained with by the receptacle of the spindle rotating with slow coupling speed. But then, the usual connection between a tenon block and a groove between receptacle and tool holder cannot act, so that there is no connection between tool holder and spindle that is able to work.
Apart from that, in such undefined situations a damage of the segments may occur.
It is therefore an object of the present invention to improve a spindle of the kind mentioned at the outset in such a way that the afore-mentioned problems are eliminated. In particular, a safe coupling of the tool holder into the spindle is to be reached and damages to the elements of the clamping mechanism are to be avoided.
According to the invention, this object is achieved with the spindle of the kind mentioned at the outset by providing a second guiding, by means of which the at least one segment is held in a defined way in the second operation position as well as in any interposition between the first and the second operation positions.
The object underlying the invention is, in that way, completely achieved.
The second guiding guarantees namely that all segments are always in a defined position, i.e. also and particularly in the two operation positions which correspond to the radial end positions. It that way, it is guaranteed that a new tool holder can always be inserted on defined conditions with its shaft into the receptacle of the spindle and, there, after short locating run of the spindle receptacle with the coupling speed, also the interlocking connection between tenon block and groove can be made, so that the tool holder is not only clamped in the correct angle position, but also a reliable non-positive connection in the region of the conical seat between shaft and receptacle is reached.
In a preferred embodiment of the spindle according to the invention, the at least one segment extends alongside the axis, whereby the first guiding engages on both axial ends and the second guiding engages on only one end of the segment.
This embodiment has the advantage that the second guiding can be limited to the necessary minimum and thus an inexpensive and constructively simple solution is possible.
In a preferred development of the embodiment mentioned before, the second guiding acts on the axial end of the at least one segment, which end is facing away from the receptacle.
This embodiment has the advantage that the elements of the second guiding can be put to the rear in the spindle so that no disturbing installations are necessary in the front region.
In a further preferred embodiment of the invention, the first guiding acts, in the second operation position, only at the axial end of the at least one segment, which end is facing away from the receptacle.
This group of features corresponding to the prior art has been successful in praxis and means that the measures provided according to the invention can also be used in other usual clamping mechanisms and can also be, if necessary, retrofitted.
In a further embodiment of the invention it is provided that the guidings are designed as oblique guidings, whereby the at least one segment has preferably an essentially circular-arc shaped form in the radial section and the oblique guidings are formed by conical bevels.
These measures have the advantage that elements known and tested per se can be used for the oblique guidings. By means of a single axially directed force, all guide movements can, in that way, be generated or deviated therefrom.
In the context of the present invention, it is preferred in a kind known per se if a plurality of segments is arranged and distributed over an outer circumference of the clamping arbor.
Then, it is also preferred, in correspondence with known embodiments, that the segments, at their end facing away from the receptacle, are held in a common crown, and that this crown is equipped with first conical bevels which act together with second conical bevels on the segments as part of the first guiding.
It holds true also in this case that it is preferably possible for this invention to keep a plurality of tested constructive elements.
This holds true, amongst other things, for the fact that the crown is axially clamped against the force of a spring, if the clamping arbor is axially shifted, whereby further preferably said spring is relaxed in the second operation position.
Finally, it is provided for such a crown, according to the invention, to have a cylindrical section which holds the spring as well as a plurality of axially protruding shoes, on which these first conical bevels are formed.
In the context of the present invention, it is now further provided for in an advantageous way that in the axial region of the crown a bushing is arranged, which bushing is designed coaxial in relation to this crown, and that this bushing is equipped with third conical bevels which act together with fourth conical bevels on the segments as second guiding.
This measure has the advantage that a particularly compact arrangement is produced, which needs not necessarily be larger in its constructive dimensions than usual arrangements with such a crown. In that way, it is possible to retrofit known systems according to the invention.
In this connection, it is further preferred if the first/second bevel is inclined diametrically to this third/fourth bevel.
This measure has the advantage that by forces, which are directed in different directions, the desired holding of the elements in the interpositions and in the second operation position can be safely ensured.
It is particularly preferred in this connection if the bushing is arranged axially fixed.
This measure has the advantage that a particularly simple sequence of movements is produced, since, for the second guiding, no extra force source or force deviation is required, it is sufficient, rather, if the bushing is supported by the spindle.
According to two preferred variations of these embodiments, the crown can either be radially on the outside and this bushing radially on the inner side or vice versa. Both variations have their own constructive advantages which may be used depending on the case.
In the case of a crown radially on the outside, it is further preferred if the latter is guided in a bore of the spindle, as it is known from other arrangements of that sort.
Further advantages can be taken from the description of the enclosed drawing. It is understood that the features mentioned above and those yet to explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without leaving the context of the present invention.